The invention is related to the field of cooling conveyors, and in particular to a flexible nozzle deck for cooling conveyors with process optimizations.
In a conventional rolling mill installation, hot rolled steel rod emerges from the last roll stand of the mill at a temperature of about 750°-1100° C. The rod is then rapidly water-quenched down to about 550°-1000° C. in a series of water boxes before being directed by driven pinch rolls to a laying head. The laying head forms the rod into a continuous series of rings which are deposited on a cooling conveyor. The conveyor has driven table rollers which carry the rings in a non-concentric overlapping pattern through one or more cooling zones. The conveyor has a deck underlying the rollers. The deck is interrupted by slots or nozzles through which a gaseous cooling medium, typically ambient air, is directed upwardly between the rollers and through the rings being transported thereon. The cooling air is driven by fans connected to the nozzles via plenum chambers. The thus cooled rings drop from the delivery end of the conveyor into a reforming chamber where they are gathered into upstanding coils.
The non-concentric overlapping ring pattern has a greater density along edge regions of the conveyor as compared to the density at a central region of the conveyor. Therefore, a greater amount of air is directed to the edge regions of the conveyor to compensate for the greater density of metal at those regions. Typically, this is achieved by increasing the nozzle or slot area at the edge regions. This can be accomplished by locating short slots or nozzles at the edge regions between longer slots or nozzles which extend across the full conveyor width. Alternatively, full width nozzles or slots may be employed exclusively in conjunction with mechanical means such as vanes, dampers, etc. (not shown) in the plenum chambers to direct more air to the conveyor edge regions.
The cooling path through metallurgical transformation is a function of the air velocity and the amount of air (among other factors) applied to the rod. Thus, as the rod is conveyed by the table rollers over successive mutually spaced slots or nozzles, the resulting intervals between coolant applications produce a stepped cooling path.
With a greater number of coolant applications at the edge regions as compared to the central region, the non-uniform intervals between successive coolant applications will result in one cooling path at the edge regions and a different cooling path at the central region. These different cooling paths cause different rod segments to pass through transformation at different temperatures and at different rates, resulting in non-uniform metallurgical properties along the length the rod.
A related disadvantage of conventional air distribution systems is the “hard” transition from high air velocities at the conveyor edge regions to lower air velocities at the central region. Where different numbers of nozzles are located at the edge and central conveyor regions, the edge nozzles supply air only over a discrete portion of the total width of the steel rings being cooled. There is a sudden change from intense air cooling to no air cooling at the transition between the edge and the central regions. In the case of nozzles which span the entire width of the conveyor as used in conjunction with vanes or dampers to direct more flow to the edges, there is also a “hard” transition from high flow at the edges to lower flow in the center. This is a result of the presence of dividers in the plenum chamber upstream of the nozzles, which channel the air from the fans to the nozzles.
In other prior art systems apply cooling air to all ring segments at regularly spaced intervals, coupled with a decrease in the air flow rate at the central region of the conveyor, where ring density is lower than that at the conveyor edge regions.